1. Field of the Invention
This invention concerns a method of and apparatus for igniting internal combustion engines other than diesel engines.
2. Description of the Prior Art
In internal combustion engines using conventional electric spark ignition systems, engine misfire occurs inevitably, upon igniting evaporated fuels in engine cylinders by way of spark discharges, at a rate as high as 20-30% but it is considered impossible to completely eliminate such undesired phenomena in view of the mechanical structure of the ignition apparatus. Such misfire in engine ignition reduces the engine power below rated levels and produces noxious substances in exhaust gases due to incomplete combustion of fuels as well.
The engine misfire is mainly attributable to the defective operations in the electric system of the ignition apparatus and the reasons or the mechanisms thereof have substantially been recognized. In the conventional engine ignition apparatus, a contact breaker and a distributor interlocking with the rotation of an engine crank shaft are employed as a mechanism for producing electric ignition sparks at a high voltage in engine cylinders in synchronization with the rotation of the crank shaft, wherein electric discharge at high voltage prepared from a DC power source such as a battery or a dynamo generator under the action of a contact point which is turned on and off by the operation of a cam of the contact breaker is distributed by way of a distributor to an ignition plug in each of the engine cylinders to thereby ignite evaporated fuels in the cylinder.
However, the mechanical operations of the contact breaker, distributor and the like can not always correspond smoothly and reliably to the high speed rotation of the engine crank shaft and, therefore, power supply through the route of discharging current at high voltage from an ignition coil to each of the ignition plugs is often interrupted occasionally. If the misfire occurs at high frequency during rotation of the engine due to such a reason, it indeed decreases the average power of the engine, although not causing complete stopping of the engine, usually by about 20-30% of the rated power corresponding to the frequency of the misfire.
In view of the foregoing, improvements have been made for the contact breaker or the distributor but no drastic solution can be obtained in the conventional ignition apparatus using mechanical ON-OFF contact actions for the step-on of a low DC voltage source in the ignition coil and, thus, the technique capable of eliminating the misfire in engine ignition apparatus has not yet been developed.
Furthermore, in the conventional engine ignition apparatus, evaporated fuel, for example, a mixture of gasoline and air is compressed to a high pressure in the engine cylinder by the action of a piston or the like, and an electric current at high voltage sent from the contact breaker and distributed by way of the distributor to each of the ignition plugs is discharged only once at the final stage of the compression step, that is, at an optimum explosion timing to thereby ignite and fire the fuel in the cylinder.
However, since the electric spark discharge at the explosion step in the cylinder is produced only for once during a brief moment of the compression step of the piston actuated by the high speed rotation of the engine, if an electric spark discharge is produced, it may sometimes result in only incomplete combustion of the fuel.
The ignition or firing phenomena caused by the spark discharge in the engine cylinder will now be considered more specifically. Sparks produced by an electric discharge between a center electrode and a grounded electrode of the ignition plug ignite combustible particles of the gaseous fuel in contact with the sparks and the ignition propagates from the initially ignited particles to each of adjacent combustible particles successively in an extremely brief period of time, that is, explosion occurs. However, since the electric discharge is produced only once per one compression step, not all of the combustible particles are fired at once but only the particles adjacent to the path of the electric spark are ignited initially and then adjacent combustible particles are fired successively. Since the time required for firing all of the combustible particles in the cylinder, although short in itself is relatively long as compared with an extremely high speed of the piston, the subsequent exhaustion step may sometimes start before all of the combustible particles are fired in the explosion step. This leads to incomplete combustion of fuels and, therefore, produces undesired noxious substances in the exhaust gases.
At present, a strict legal regulation is imposed on the discharge level of such noxious substances contained in the engine exhaust gases and various coutermeasures have been taken for meeting the standard. However, most of them concern the provision of catalytic converters for the after-treatment of the exhaust gases or the recycling of the exhaust gases to the engine cylinder and no effective means have yet been developed for the improvement of the disadvantages of the engine ignition apparatus which are responsible for one of the major factors of incomplete combustion.
As described above, although conventional ignition apparatus for the internal combustion engines involve inherent drawbacks lacking in the smooth and reliable ignition for the engine, such drawbacks have been considered inevitable to some extent and no effective technical ideas for overcoming them have yet been proposed.